Horizontal cracks in blockwork

[Fireblade170]

Hi I'm after some advise to remedy a problem I have. Not long moved into a house built in the eighties with block work internal walls and brickwork outer, the problem is a crack appears in the mortar joint of the top course of block work in one of the bedrooms during the summer only. This is probably due to the roof expanding as this corner is south east facing and thus gets most of the sun, the blocks are then pushed enough to open a crack approx 1mm wide and you can feel a step in the plaster surface. I have thought of chiselling the plaster back to the block work and screwing steel braces bridging the mortar joint on the top course thus bracing the top 2 courses together but I'm worried that the crack will then appear on the second course mortar joint. I have also thought of dot n dab plaster board on the effected corner and just allowing the movement to happen under the plaster board but this is more work as 2 walls are effected one of which has a window. If anyone has come across this problem and achieved an effective repair I'd be interested in what worked. Your comments are appreciated, thanks

 

[footprints]

Not a "cure" but if the crack is near the ceiling line, light weight coving is fairly flexible fitted with a flexible adhesive it might take up the movement.

Not like the old polystyrene that shows the texture, modern stuff is very smooth and looks like plaster if well done.

footprints